what is Synchronous Data Link Control (SDLC) ?


what is Synchronous Data Link Control (SDLC) ?

In: Technology

It’s an old way for devices to talk to one another through wired connections, created by IBM and pretty much only used by IBM.

At one point, there were a lot of competing standards (SCSI, Ethernet, Econet, Token Ring, LocalTalk, RS-232, IEEE 488), but most of these standards have died out, and most devices today talk to each other using Ethernet, or new standards like Wi-Fi (802.11) or ZigBee.

SDLC lives on in a small niche of connecting industrial devices and sensors to their controllers, as part of the BITBUS standard.

SDLC (Synchronous Data Link Control) was invented by IBM to be a Layer 2 (data link layer) protocol allowing computing devices to communicate with each other in their SNA network architecture.

In the middle-1980s the ISO international standards organization (now named the ITU) codified SDLC into a standard protocol, named HDLC (High-level Data Link Control). HDLC has since become the parent protocol for a number of extensions that are still in pretty wide use today.

The PPP (Point-to-Point Protocol) was largely modeled after HDLC, but added extensions, and these days, while PPP is not frequently used by consumers to connect to the Internet via dial-up modems (which themselves used the V.42/LAPM error correction protocol, derived from HDLC), it is used pretty widely in devices like DSL modems. Other equipment commonly used to connect offices and larger organizations together or to the Internet also make use of PPP.

So SDLC, through various child protocols and imitations, is in wide use today, though usually deeper within other protocols that make it less noticable to the average person.